In rotary sheet printing presses for optional one-side printing or two-side printing, arrangements are necessary to shift over the control of the sheet running, so that in one case the sheets, held only by their leading edge, are conducted through the rotary sheet printing press and, in the second case, can be turned during the sheet running from their leading edge to their rear edge. In the technology of sheet turning, it is necessary to provide both grippers that can be swung with respect to one another for the transfer of the sheet end on a turning drum, and also to make it possible to shift the gripper opening point on the turning drum in such a way that the transfer time point corresponds to the running of the sheet end. For this purpose, turning cams have to be switched on the turning drum and the gripper opening cams shifted in correspondence to the shift-over of the sheet ends relative to the turning drum or with a correspondingly shifted opening point of the grippers.
In German patent application DE-AS No. 2,133,693 there is described a device for the control of the grippers of a sheet-transfer and turning drum of a multicolor rotary sheet printing machine. In this turning drum, there are turning cams and gripper opening cams. In normal operation of this rotary sheet printing press, the turning cam is out of engagement. For the gripper opening there are special cams in each case for one-side printing and for the two-sided printing operation. The turning cams and the gripper opening cams are shiftably disposed and coupled with one another over a special rod system. For the shift-over of the machine from one-side printing to two-side printing operation, the rod system is unlocked and shifted axially via a hand grip, so that simultaneously the turning cam and the gripper opening cam are axially shifted. The turning cam then comes into engagement, while the gripper opening cam for one-side printing comes out of engagement and the gripper opening cam for two-side printing likewise comes into engagement. Despite the relatively simple operation of the above-disclosed device, the time and expenditure of effort for the shift-over operation is relatively high. Moreover, it will be recognized that an operating procedure of several manual operations is necessary first for the shift-over of the turning cams and gripper opening cams.